Re: [PATCH 5/5] Create a hole in high linear address space

[Chris Wright <chrisw@osdl.org>]

* Zachary Amsden (zach@vmware.com) wrote:
> Allow compile time creation of a hole at the high end of linear address space.
> This makes accomodating a hypervisor a much more tractable problem by giving
> it ample playground to live in.  Currently, the hole size is fixed at config
> time; I have experimented with dynamically sized holes, and have a later
> patch that developes this potential, but it becomes much more useful once
> the exact negotiation of linear address space with the hypervisor is defined.
> 
> The fixed compile time solution is sufficient for now.

Xen moves __FIXADDR_TOP like this:

#ifdef CONFIG_X86_PAE
# define HYPERVISOR_VIRT_START (0xF5800000UL)
#else
# define HYPERVISOR_VIRT_START (0xFC000000UL)
#endif

and

#define __FIXADDR_TOP  (HYPERVISOR_VIRT_START - 2 * PAGE_SIZE)

and also adds bits to fixmap.

So this proposed mechanism isn't quite good enough.

thanks,
-chris